When you let the nozzle click off, the gas in the hose is trapped there. If you started filling with the hose full of gas, you got the metered amount you paid for. If the person before you put a fixed amount of fuel into his/her tank; let the pump shut off on its own; and then milked the remanent in the hose, that person would have gotten a cup or so of extra gas at your expense.

The consensus I have read is that the practice of milking the hose is only minimally advantageous unless you have only time to burn. I guess if you are concerned about this you could watch the person fill at the pump you plan to use and make sure that he/she doesn’t wiggle the hose and nozzle around to get the last drop. If you could find a nonselfserve station that has an attendant fill, you might get a more honest fill.

With the newer generation of pressure activated valves, all deliveries are equal. You cannot squeeze open the valve and get any gas with the pump off.

Yes, in the old days, the simple spring valve would allow the draining of the hose and people could actually fill a jug with gas by going around to all the hoses and getting every last drop.
But these days once the pump shuts off, the lack of line pressure doesn’t allow the valve to open and drain out the hose. Hence, every serving of gas is equal.
There may still be some stations with older equipment, but around the four corners I’ve not encountered any in the last ten years or so.

This generally works out OK, but if you are trying to buy a small quantity of premium gas, like for a motorcycle, you do get a significant shot of regular every time you fill up. There’s nothing you can do about it.